Like others have said, the 2012 and newer have the Pentastar engine and a few more ponies under the hood. The downside is they are a bit more temperamental compared to the previous 3.8 liter engine. I would try to avoid the 2012's due to the first year model and had some growing pains in the form of cylinder head issues. They have more than likely been corrected by now seeing as how a 2012 is now 7 years old and more than likely has 50k+miles on it but personally I would steer clear of 2012's unless you get a screamin' deal to allow some engine work/repairs if necessary.
The 2007-2010 had the older interior and the 3.8 liter engine with either the 6-speed manual or the 42RLE 4-speed automatic transmission. The engine gets a bad rap but honestly I think the 42RLE transmission is the Achilles heel of the drivetrain package. Had the 3.8 liter engine been coupled with a five, six or even the never 8-speed transmission I think it would have been a much more viable engine for the JK/JKU platform.
The 2011 is an odd-ball year as it has the older 3.8 engine/42RLE transmission yet it has the newer interior. Many people steer clear of the 2011's for this reason. When we were looking in late 2011, I was looking at 2009-2010 due to my budget constraints and the fact that I still wanted to have funds left over to actually build the Jeep and not have to drive it in stock form.
In my personal opinion, I would search for a clean virgin 2008-2011 JKU that has been taken care of and swap in an LS engine with the 6L80E transmission and really have a nice daily driver/weekend wheeler and you will be into it about the same if not less than a newer Jeep.
Mike
